1. Field of the Invention
The present invention generally relates to a mobile communication system and, more particularly, to a mobile communication system that has an active home location register (HLR) and a standby home location register which includes a database having the same contents as those of a database of the active home location register, and that has the functions of autonomously recovering from a mobile-station-location-information loss phenomenon which may be caused when the system performs switching between the active and standby home location registers in response to an occurrence of a fault.
2. Description of the Related Art
A conventional mobile communication system comprises an active home location register, a standby home location register which includes a database having the same contents as those of the active home location register, visitor location registers (VLR), mobile switching centers (MSCs), and mobile stations (MSs). When a fault occurs in the active home location register of this system, the active home location register is switched to the standby home location register which now serves as a new active home location register. Thus, the system continues operation.
The contents of the database of the standby home location register are periodically updated in such a manner as to match the contents of the database of the active home location register. Therefore, generally, even after the active home location register is switched to the standby home location register as described above, the contents of the database of the new active home location register match those of the database of an old active home location register. Consequently, it is expected that the system will continue normal operation.
As described above, the conventional system periodically updates the contents of the database of the standby home location register. However, when a fault occurs in the active home location register, the active home location register is immediately switched to the standby home location register. This results in a difference in contents between the database of the old active home location register used before an occurrence of a fault and that of the new active home location register (namely, the old standby home location register) used after the occurrence of the fault. FIGS. 1 to 3 illustrate an example of such a conventional system.
FIG. 1 shows the constitution of an example of an ordinary mobile communication network.
As shown in this figure, an active home location register (ACT-HLR) 1 and a standby home location register (STABY-HLR) 2 are connected to a network 3 including a portable telephone network and an automobile telephone network. Further, each of areas (AREAa and AREAb) 4 and 5 under the control of the network 3 is provided with a corresponding one of visitor location registers (VLRs) 7 and 9 for registering station location information on the location of a mobile station therein and a corresponding one of mobile switching centers (MSC) 6 and 8 for performing switching between the mobile stations.
In the case of this example, a mobile station (MS-X) 10, such as a portable telephone or an automobile telephone, is present in the area 4. The location of this mobile station is registered. Therefore, the mobile switching center 6 and the visitor location register 7 provided in the area 4 hold the profile (indicated as MS-X) of the mobile station 10. Further, the mobile station and the station location information thereof are respectively registered (as indicated by the expression xe2x80x9cMS-X: AREAaxe2x80x9d) in the active home location register 1 and the standby home location register 2 through the network 3.
FIG. 2 illustrates an example of the case that a fault occurs in the active home location register of FIG. 1.
That is, this figure illustrates the case in which the mobile station 10 moves from the area 4 to the area 5 and then makes a request for registration of the location thereof in the area 5, and in which the registration of the location thereof is subsequently completed. Thus, the profile of the mobile station 10 is deleted from the mobile switching center 6 and the visitor location register 7 in the area 4. Moreover, the profile of the mobile station 10 is copied from the active home location register 1 to the mobile switching center 8 and the visitor location register 9 in the area 5.
Although the latest registered location information (AREAb) of the mobile station 10 is registered in the active home location register 1, the database of the standby home location register 2 of this example is not updated yet. Therefore, the registered location information (hereunder sometimes referred to as location registration information) of the mobile station 10 is still registered in the old registration area (AREAa).
FIG. 3 illustrates an example of the aforementioned conventional location registration sequence.
Incidentally, it is supposed herein (and in the following descriptions of examples) that IS-41-C (Interim Standard 41 Revision C) standardized in north America is employed as a signal protocol for a mobile communication system, in which signals are transferred through a signal network. The aforementioned protocol is generically called MAP (Mobile Application Protocol/Part).
As shown in FIG. 3, the mobile station 10 moves from the area 4 to the area 5 and then transmits a location registration request message to the mobile switching center 8 in the area 5 in which the station 10 is present (step S101). Subsequently, the mobile switching center 8 transmits a location registration request message (REGNOT) concerning the mobile station 10 to the visitor location register 9 (step S102), which then transmits the location registration request message to the active home location register 1 (step S103).
After receiving this message, the active home location register 1 transmits a location registration canceling message (REGCANC)to the visitor location register 7 (step S104) in a current registration area (AREAa). Then, the visitor location register 7 transmits a location registration canceling request message to the mobile switching center 6 (step S105). If the mobile switching center 6 has the profile of the mobile station 10, the center 6 deletes this profile and returns a location-registration-canceling-request response message (regcanc) to the visitor location register 7 (step S106).
When the active home location register 1 receives the location-registration-canceling-request response message from the visitor location register 7, the register 1 updates the registration area (AREAa), in which the profile of the registered mobile station 10 is registered, to the latest registration area (AREAb) and then transmits a location-registration-request response message (regnot) to the visitor location register 9 provided in the area 5 (steps S108 to S110). Subsequently, the visitor location register 9 provided in the area 5 registers the profile of the mobile station 10, which is contained in the location-registration-request response message, therein and transmits a location-registration-request response message to the mobile switching center 8 (steps S110 to S112). Similarly, the mobile switching center 8 registers the profile of the mobile station 10 therein.
Incidentally, there are the following two manners of transmission of the profile from the home location register to the visitor location register and the mobile switching center: a) transmission of the profile as a parameter of a profile transferring message; and b) transmission of the profile as a parameter of a location-registration-request response message. Although only the manner b) has been described in the foregoing description of the aforementioned example, the manner a) may be employed instead of the manner b).
Meanwhile, FIG. 2 illustrates the case that a fault occurs in the active home location register 1, as indicated by xe2x80x9cXxe2x80x9d, after the aforementioned process. Consequently, the active home location register 1 is immediately switched to the standby home location register 2, which then starts operation as a new active home location register 2 according to old registration information corresponding to the area (AREAa), in which the mobile station 10 is not present. At this time, a state in which the new active location register 2 lacks the location registration information concerning the mobile station 10 occurs in the system.
FIG. 4 illustrates an example of a conventional incoming call sequence.
Particularly, this figure shows the case that an incoming call arrives the mobile station 10, the location registration information of which lacks the state shown in FIG. 2. As shown in this figure, when receiving, from a gateway mobile switching center (G-MSC), a location registration inquiry message (LOCREQ) making an inquiry concerning the location information on the location of the mobile station 10 (step S201), the new active home location register 2 refers to the registered location information(AREAa) concerning the mobile station 10 and then sends out a routing information acquisition message (ROUTREQ) to the visitor location register 7 provided in the area 4 (step S202).
When receiving the routing information acquisition message, the visitor location register 7 returns a response message containing an error code (xe2x80x9cERROR CODE=Unrecognized MINxe2x80x9d) to the active home location register 2 (step S204), because the visitor location register 7 does not have the profile of the mobile station 10 (step S203), which is a called station. When receiving the response message containing the error code, the active home location register 2 deletes the registered location information (AREAa) concerning the mobile station 10 (step S205) and then returns a response message (locreq) containing an error code (ERROR CODE) to the gateway mobile switching center 11 (step S206). Thus, from then on, no incoming calls can arrive at the mobile station 10 from an external device.
As described above, the conventional system has the following drawbacks:
1) No incoming calls can arrive at the mobile station whose location information is erroneously registered in the new active home location register 2.
2) The network has no means for autonomously correcting and restoring the missing location registration information.
That is, as illustrated in FIG. 4, the location information in the profile of the mobile station 10 is absent in the new active home location register 2. Thus, no incoming calls can arrive the mobile station 10. Further, it is necessary, for returning the mobile station 10 from the current state in the system to an incoming enabling state that the location of the mobile station is reregistered in the new active home location register by moving the mobile station 10 to another location registration area and then (normally) registering the latest location of the mobile station 10 in this location registration area, as illustrated in FIG. 3.
Thus, the conventional system has a drawback in that an incoming disabling state of the mobile station 10 continues for a long time until the location of the mobile station 10 is registered in the new active home location register 2. Moreover, the conventional system has another drawback in that the network has no means for positively remedying such a state of the mobile station 10.
Accordingly, in view of the drawbacks of the conventional system, an object of the present invention is to provide a system and method for taking the following two measures to remedy a mobile station, the latest location registration information of which the system lacks, by switching between the home location registers. That is, an object of the present invention is to provide a system and method for retrieving mobile-station location registration information, which can enable incoming calls to such a mobile station and which enables the network to autonomously correct the location registration information of the mobile station.
Further, another object of the present invention is to provide a system and method for relieving mobile-station location registration information, which can correct and restore not only the missing mobile-station location registration information by switching between the home location registers, but the missing mobile-station location registration information of an ordinary mobile station.
To achieve the foregoing objects, according to an aspect of the present invention, there is provided a mobile communication system having home location registers, visitor location registers, mobile switching centers, and mobile stations. In this mobile communication system, each of the home location register comprises a rerouting information acquisition section for performing routing information acquisition processing when receiving, in response to a routing information acquisition message which is sent out to one of the visitor location registers, a response message indicating that a corresponding one of the mobile stations is not present.
Further, according to another aspect of the present invention, there is provided a mobile communication system having home location registers, visitor location registers, mobile switching centers, and mobile stations. In this mobile communication system, if one of the visitor location registers having received routing information acquisition message from one of the home location registers has no profile of a corresponding one of the mobile stations therein, the one of the visitor location registers performs routing information acquisition processing on another of the visitor location register and has a rerouting information acquisition section for informing the one of the home location registers of a result of the routing information acquisition processing.
Furthermore, according to still another aspect of the present invention, there is provided a mobile communication system having home location registers, visitor location registers, mobile switching centers, and mobile stations. In this mobile communication system, each of the visitor location registers has a location information relief processing section for sending to one of the home location registers a request to verify location registration information. The one of the home location registers has a location information verification processing section for verifying and collating the location register information with location registration information held therein in response to the request from the location information relief processing section and for correcting the location registration information according to a result of verifying and collating thereof.